Patent document 1 discloses a fastener having a lock function. More specifically, a female snap 1 has: a stopper 5 upwardly urged by a spring member 12; an engagement member 6 shaped as shown in its FIG. 2; and an elastic ring 10 mounted on an engagement portion 17 of the engagement member 6. FIGS. 6(a) and (b) disclose snap-in process of the male snap 2 with the female snap 1. When the male snap 2 is removed from the female snap 1, a key bar 22 is utilized to push the stopper 5 down as shown in FIG. 6 (d). Accordingly, the engagement portion 17 of the engagement member 6 is allowed to expand freely externally, thereby achieving the removal of the male snap 2 from the female snap 1.
Patent document 2 discloses a female body 5 in which an integrated part having a fixed portion 7 and a fitting projection 9 and made of molding material of an elastic rigid resin is housed in a housing 15. It is described that, when a male body 3 is pressed therein, the fitting projection 9 is much further bent in the press-in direction and the fixed portion 5 is expanded toward the surrounding side tube 20 of the housing 15, thereby an easier press-in of the male body being secured.
Patent document 3 discloses a female part provided with a circular groove 5 at a surrounding wall 3 rising from the periphery of a base plate 2, wherein when an inner surrounding wall portion 3a is elastically transformed radially outwardly, only its top end contacts with an outer surrounding wall portion 3b, preventing its further elastic transformation. As shown in its FIG. 1, a bulge 7 is provided generally continuously in the circumferential direction at the inner side of the inner surrounding wall portion 3a, thereby enough fitting against a protrusion of a male part being secured.
Patent document 4 discloses a female member in which a wave shaped circular engagement spring 7 having outer ridges 9 and inner ridges 10 is provided in a housing 6, and a slit 8 is provided at a portion other than the top 10A of the inner ridge 10.